Such a resonator of small dimensions is disclosed in the prior art document U.S. Pat. No. 4,384,232, which is incorporated herewith by way of reference. This document discloses a tuning fork resonator formed by a base and two vibrating arms protruding from the base. Each arm carries metallization which forms central electrodes on the opposite main surfaces and lateral electrodes along the edges of each arm. The central electrodes of one arm are connected to the lateral electrodes of the other arm and to one pole of the supply. The other central and lateral electrodes are similarly connected to the other pole of the supply. Electrodes are subjected to electric fields to make the arms vibrate.
The central and lateral electrodes are arranged with a fixed spacing there between so that these do not short-circuited one another. Nevertheless, this spacing is chosen as thin as possible in order to have better crystal impedance for the resonator. As a result, if even a small amount of dust falls between the central and lateral electrodes or if some gas is present in the vicinity of the electrodes, a short-circuit is likely to occur, and the vibration of the vibrating arms may then malfunction.
Some existing solutions of the prior art consist in providing a short-circuit prevention section formed between the central and lateral electrodes of each vibrating arm and arranged in the form of an insulating film that may be either located between the central and lateral electrodes or arranged to cover both the central and lateral electrodes. However, although these prior solutions effectively prevent short-circuits between central and lateral electrodes, they further present several drawbacks, and in particular, they require to readapt the whole design of the resonator in order to keep the same characteristics such as resistance and crystal impedance of the resonator. This required design adaptations renders the making process more expensive which is not desirable for such mass produced item.